The experience of breast cancer often evokes a great deal of stress, which can compromise immunological functioning and quality of life. The aim of this pilot study is to provide initial assessment of the efficacy of a stress reduction intervention program for women with breast cancer on quality of life and immunogical functioning. This proposal focuses on Mindfulness-based Stress Reduction (MBSR), a well-established cost-effective stress reduction intervention, recently introduced into Western medicine. The literature demonstrates the effectiveness of MBSR to improve ability to cope with stress and enhance psychological and physical well being. Despite this, there are no studies in the literature examining the effects of MBSR for women with breast cancer. To address this, we propose a 2-year exploratory effectiveness study involving a well-controlled design comparing MBSR to an individually monitored control group. We will use self-report questionnaires and immunological parameters to assess response to MBSR. Specific aims are: 1) to explore the effects of MBSR on psychological, social and somatic functioning for women with Stage II breast cancer within one year post treatment, and 2) to explore the effects of MBSR on immunological functioning for women with Stage II breast cancer within one year post treatment. The hypotheses are: 1) MBSR will produce greater improvement in the experimental group on standardized measures of psychological, social and somatic functioning as compared to the control group, and 2) MBSR will produce enhanced immune functioning in the experimental group as compared to the control group. This study will advance our research program on biopsychosocial interventions for women with stage II breast cancer.